1. Field of the Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a method for forming a strained semiconductor device and to a method for forming an S/D region based on the former method.
2. Description of the Related Art
As the dimension of semiconductor device is greatly reduced, strain effects are often utilized to increase carrier mobility and improve the performance of the devices. For example, a strained source/drain (S/D) region of a Si-based PMOS transistor can be formed to increase the hole mobility and reduce the resistance of the S/D region. The stained S/D region can be formed by forming an opening at the corresponding position of an N-type silicon substrate and then filling boron-doped SiGe in the opening with selective epitaxy growth (SEG).
However, since the PN junction of the S/D region coincide with the interface between the N-type substrate and the P-type epitaxy SiGe layer in the above method, the current leakage through the PN junction of the S/D region is a problem.